Displays are important components of computers as they provide visual data for interaction with computer users. In computer systems that use CRTs or the like, the voltage that is used to accelerate electrons towards the phosphor dots of the screen surface determines the intensity, or brightness, of the display. In portable computers, liquid crystal displays (LCD) or the like are illuminated by a backlight to enhance contrast and increase the visibility of what is displayed. The intensity or brightness of a computer display is typically adjustable by a user. This adjustment is important for computer users because all users do not have the same quality of eyesight. Specifically, some users are more light sensitive and reduce the brightness of the display so the glare of the screen does not irritate their eyes. Others require greater brightness so they can clearly see what is displayed on the screen without squinting or straining their eyes. Consequently, most computer displays include variable switches so users may increase or decrease the display brightness depending upon the needs of their eyes.
One factor that contributes to the need for adjusting the brightness of a display is the ambient light level of the environment where a user views the screen. In ambient light of low intensity, users probably prefer lower brightness levels for the display as most can view the screen adequately at a relatively low brightness level for the display. To address the need to adjust the display brightness according to ambient light changes, systems have been developed to sense ambient light levels and adjust the display brightness level accordingly. Adjustment of display brightness level in response to ambient light changes is especially important for computers that are powered by a battery source. A substantial portion of the energy drained from a battery is used to illuminate the display. Thus, operation of the display at the lowest acceptable level for ambient light conditions significantly improves the battery life for a portable computer. A system for adjusting display brightness with reference to ambient light is disclosed in U.S. Pat. No. 5,760,760. The system of the '760 patent includes one or more light sensors for determining an ambient light level and adjusting the brightness of the display to a predetermined brightness level that improves the length of battery life. The patent also teaches that the system may include a neural network for “learning” user-defined brightness levels for ambient light range so that the user-defined brightness levels may be used to override the predetermined brightness level. This learning may “take into account” previous user-defined brightness levels and may adjust the display brightness level accordingly.
While the '760 patent addresses the issue of ambient light changes and the “learning” of user-defined brightness levels that differ from the predetermined brightness levels, it fails to account for the differences in the eyesight of different users. If the previous user for a computer is different than the current user of a computer then the system of the '760 patent will combine the level selected by the current user with that selected by the previous user and “learn” that level. If the previous user had relatively weak eyesight, the brightness level is probably appreciably greater than that selected by a user having stronger eyesight. Consequently, the level “learned” is a level that is adequate for neither the first or the second user. That is, the system of the '760 patent assumes the user remains the same and that typically is not true of the use of many computers.
What is needed is a system that can adjust the brightness level of a computer display to a level that corresponds to the eyesight of a current user.